Treatment of crude tar acids fractions



Patented Jan; 29, 1946 UNITED ST T T OFFICE TREATMENT OF CRUDE TAR ACIDS FRACTIONS vimm Molinari, North Piainfleid, N. 1., assignor to Bakelite-Corporation, a corporation of New Jersey No Drawing. Application September 11, 1943,

- Serial No. 501,992

isolation from crude tar acids of phenols suitable for reaction with formaldehyde to yield resins; these phenols comprise phenol (monohydroxy benzene) and the homologous methyl phenols which include cresols,xy1enols, trimethyl phenols and tetramethyl phenols. At present it is the common practice to recover these phenols from crude tar acids produced in the high temperature carbonization of bituminous coals; and the phenols are obtained by washing the tar acids with aqueous caustic soda, separating by decanting from the oily layer the water layer carrying the phenolates in solution, concentrating the water layer to eliminate oily and pyridine impurities, and liberating the phenol mixtures by means of carbon dioxide or sulfuric acid. The mixtures of phenols are usually fractionated under vacuum into phenol, cresol and xylenol cuts, for each out has a definite reactivity with formaldehyde.

Besides the crude tar acids obtained in high temperature coal distillation, there are large potential but unused sources of phenols for resin production. Among these sources are the crude tar acids produced in the carbonization of lignite and hard woods such as maple, oak, redwood and Douglas fir; other sources are the tar acids resulting from low temperature distillation and the hydrogenation of coal. Common to the tar acids from these sources is the presence therein of the alkyl ethers of dihydroxy benzenes or alkoxyphenols, such as guaiacol and methyl guaiacol; the ethers or alkoxy-phenols in general are present in amount to constitute from 5 to per cent and to impart an increase in the specific gravity to about 1.05 to 1.07 to mixtures of phenols separated from the crudetar acids. The'ethers, however, are well-known inhibitors of the resin-formin: reaction of phenol and the methyl phenols with formaldehyde; and if present in resins incorporated with drying oils to form varnishes,

, they act as strong retardants on the drying of the varnish coatings to extend the drying period many times the normal period. Accordingly their elimination is necessary before the phenol mixtures can be usedfor reslnproduction. In a co- I stituteimpurities, such as neutral oil, sulfur comfrom the phenols of other compounds that'conpounds including mercaptans, nitrogen bases (py idine), thiophenols, etc.

It has been found that the foregoing objects carbonization; l5

(2) Heating the aqueous phenolate solution to concentrate and raise the mass to a temperature that causes substantial dehydration and fusion of the mass; and

(3) Blowing the molten masswith a predetermined quantity of air carrying a definite'proportion of water vapor.

The residue remaining after blowing is dissolved in water, acidified and rectified to yield a mixture of free phenols. Phenol mixtures, so isolated from crude tar acids resulting from the distillation of hard woods, etc. and containing methoxy phenols, are found to have substantially the specific gravities and rates of reactivity with formaldehyde that characterize free phenol mixtures of the same boiling ran e obtained from crude tar acids resulting from high temperature coal distillation:

The phenolates, prepared according to step (1), are concentrated in step (2) by boiling oif water and continuing the heating to the fusion temperature of the crudephe'nolate. It has been found essential to the effectiveness of the succeeding pending application Serial No. 324,322 filed March 16, 1940, there is disclosed a method for the elimination of such ethers, and the present application is a continuation-in-part thereof."

The invention claimed herein provides for the dealkylation of the ethers present in the crude tar acids without the isolation'of objectionable step ofhblowingthat themass beat a fusion'or melting temperature, generally ranging from about 280 to 360 0., though in some cases it may be as low as 160 or 210 C.

The step (3) of blowing with air carrying a definite. proportion of water is accomplished by bubbling the air through water at apredetermined temperature whereby the air becomes saturated at that temperature; bubbling through water at about. 0., as a rule, has been found to supp y the proportion of water required and to maintain the mass in the condition of concentration and fusion without the mass becoming unduly dry and without increasing the fusion temperature. At the high fusion temperatures emphenols. at the same time it'sccures the removal ll, and t 8 therefore c a y to 8 9 e r 0 before such decomposition begins; this is determined by preliminary experiment and analysis.

During the blowing step (3) at the fusion tem perature by the air stream carrying water vapor, the alkoxy groups are split oif by hydrolysis as is 7 shown by the alcohols collected in the condensate; in fact the action is found to be quantitativeand tamer: t9; 2

with formaldehyde, and-the odors'c'hara .6teristic -1 of the tar acids of wood carbo'nization were abrapid. In addition the 'oifensi-ve odor due 'captans and other sulfur compounds disappears; and remaining objectionable impurities are removed, orthose that remain have such high boil- 2,sos,7oo'

tar acids prepared fromtar of high temperaturev ingpoint in comparison with the useful phenols 1 that the latter are readily separated by distillation following acidification and rectification.

In a German Patent-No. 584,857 to-Meyer it has been proposed to purify phenols obtained in the distillation of a form of lignite, according to the example, by passing a cold air current for several hours through a caustic soda extraction of tar fraction, thereafter steam is introduced while the solution is heated in an oil bath to 220 C. to drive off impurities, the solid residue is dissolved in water and the phenolate solution is acidified to 'yield a cresol fraction. The impurities mentioned in the patent are dihydroxy benzenes and mereaptans which are attacked by oxidation at ordinary temperatures, as the patent acknowledges, and some basic oils having the odor of quinolines and probably hydrated in the course of the steam distillation.

Such a process, however, does not cause de-,

alkylation of alkoxy phenols or ethers. vOxidation alone is not operative for the purpose, for at I room temperature no such reaction takes place;

and, if the mass is elevated to fusion or meltin temperatures, the oxidation becomes energetic with decomposition and cracking into high-=boiling and tarry products constituting a loss that may reach 40 to per cent of the original mass. Nor is steam distillation alone at fusing or melting temperature of any benefit, as far as the split.- ting-off of the alkyl groups of the ethers is concemed; while the action is apparently one of hydrolysis as indicated by the alcohols found in the distillate, steam alone is not enough and oxygen is also required. Essential to th present invention, therefore, is the conjoint passage of. steam and air through the mass at fusion ormelting. tem- Derature.

Emample. Four thousand (4000) parts of tar acids with a boiling range between 200 C. and 250 C. separated from tar obtained by carbonizing redwood showed a methoxy content of about 6 per cent; when rectified for analysis, a fraction boiling between 200 C. and 205 C. had a methoxy content of 7 to 7.5 per cent and a specific gravity at 15.6 C. of 1.05 to 1.076, and a fraction boiling between 220 C. and 225 C. had a metho y content of 7.5 to 8 per cent and a specific gravity at 15.6 C. of 1.06 to 1.07.. The crude tar acids were dissolved in an aqueous solutioncontaining 1200 parts of caustic soda, and the water solution coal carbonizations; moreover, the fraction had no guaiacol odor and contained no methoxy groups and therefore could be tested for metacresol by the Raschig methods, which was impossible with theoriginal tar acids because. of the g-uaiacol present. The fraction collected at 220 0,, showeda much impIWedIeiictivlty drogen on the ring. The process is not restricted to tar acids of the example or to the splittin off of methoxy groups; it is generally applicable to other sources of tar acids, such as those obtained from lignite and low temperature coal distillation, that contain objectionable amounts of the ethers, and applicable to the dealkylatlon of other alkyl-phenol ethers. The character and amounts of phenols and other ingredients present in the tar acid fraction treated in general controls the temperature to which the mass is raised for concentration of the water content and melting; as indicated, melting may be attained at temperatures as low as 160 C. to 180 -C.'for fractions collected within a correspondingly low boiling range and substantiallydehydrated to the extent of about per cent or more. The amount of air saturated with water vapor at about 90 C. required for the dealkylation varies with the alkoxy-phenol content, and it can be determined by a preliminary analysis on a sample; but in eneral it ranges from about 10 to 15 cubic feet per gallon of tar acid fraction treated by the process.

The dealkylation of the ethers probably results in the formation of caustic soda compounds of di- 'hydroxy benzenes, and particularly of catechol under the described conditions of concentration and melting. These are likewise undesirable;

but apparently they become oxidized, since they soda and separating the aqueous layer, heating the aqueous. layer-to substantially dehydrate and melt the mass. and p ssing through the molten mass a current of air containing water vapor in of the phenolates was concentrated by evaporation while being agitated When the molten mass reached a temperature of 280 0., acurrent of 'air 6 that had been previously bubbled through water heated to 90 C. was blown through the molten mass for about an hour until 15 cubic feet of air per gallon of tar acids used passed 'therethrough. and the temperature increased to 300 C. to 320 C. The residue remaining in the retort was dissolved in water, acidified, and then fractionallydistilled. The fraction collected at 200 C. to 205 0. had a specific gravity of 1.033 to 1.035, and this is very close to that of a cresol cutobtained from amount to cause dealkylation.

2. Process of treating a crude tar acid fraction v obtained in the carboniz'ation of wood containing a methoxy-phenol which comprises extracting the acid content by aqueous caustic soda' 5 and separating the aqueous layer, heating the aqueous layer to substantially dehydrate and melt themass, and passing through the molten mass aboutjfifteen cubic feet of air per gallon of the tar acid fraction previously bubbled through water at C.

3. Process of dealkylating an alkyl-phenol ether which comprises reacting with, sodium hydroxide in aqueoussolution, heating the solution to substantially dehydrate and meltthe resulting mass, and passing through the"molten mas: o

a,sos, 'i'oo" 3 current of air containing water vapor in amount to cause dealkyiation.

4. Process of deaikyiatina an alkyi-phenol ether which comprises hydroiyzing a concentrated and molten mass or a sodium phenolate oi the ether by passing through the. mass a current of air containing water vapor.

5, Process of dealkylating an aikyl-phenol ether to a corresponding phenol which comprises hydrolyzing a molten mass of a sodium phenolate of the ether by passing through the mass a current otair containinzwater vlpcnandaciditying 19 tion. and acidifying the mass to tree the phenols.

VI'I'IORIO MOLINARI. 

